Apoptotic cell death is an important cause of neuronal injury in experimental Venezuelan equine encephalitis virus infection of mice

Mice develop a fatal encephalomyelitis after infection with the Trinidad donkey strain of Venezuelan equine encephalitis (VEE) virus. Adult mice were inoculated intraperitoneally with VEE virus and the brains were examined at different time points. Morphological changes were assessed by histological staining. VEE virus antigen was detected with immunoperoxidase staining, and DNA fragmentation was evaluated in situ using the terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL) method. VEE antigen was found in many areas of the brain and it was prominent in neurons. There were mild associated inflammatory changes. DNA fragmentation was demonstrated in many of these areas using TUNEL. In areas with TUNEL staining, morphological neuronal changes ranged from nuclear chromatin condensations to nuclear and cellular fragmentation, which are characteristic of apoptosis. There is strong morphological and biochemical evidence of apoptotic cell death in this experimental model of VEE virus infection.

Human respiratory input impedance between 32 and 800 Hz, measured by interrupter technique and forced oscillations

Respiratory input impedance (Zin) over a wide range of frequencies (f) has been shown to be useful in determining airway resistance (Raw) and tissue resistance in dogs or airway wall properties in human adults. Zin measurements are noninvasive and, therefore, potentially useful in investigation of airway mechanics in infants. However, accurate measurements of Zin at these f values with the use of forced oscillatory techniques (FOT) in infants are difficult because of their relatively high Raw and large compliance of the face mask. If pseudorandom noise pressure oscillations generated by a loudspeaker are applied at the airway opening (FOT), the power of the resulting flow decreases inversely with f because of capacitive shunting into the volume of the gas in the speaker chamber and in the face mask. We studied whether high-frequency respiratory Zin can be measured by using rapid flow interruption [high-speed interrupter technique (HIT)], in which we expect the flow amplitude in the respiratory system to be higher than in the FOT. We compared Zin measured by HIT with Zin measured by FOT in a dried dog lung and in five healthy adult subjects. The impedance was calculated from two pressure signals measured between the mouth and the HIT valve. The impedance could be assessed from 32 to 800 Hz. Its real part at low f as well as the f and amplitude of the first and second acoustic resonance, measured by FOT and by HIT, were not significantly different. The power spectrum of oscillatory flow when the HIT was used showed amplitudes that were at least 100 times greater than those when FOT was used, increasing at f > 400 Hz. In conclusion, the HIT enables the measurement of high-frequency Zin data ranging from 32 to 800 Hz with particularly high flow amplitudes and, therefore, possibly better signal-to-noise ratio. This is particularly important in systems with high Raw, e.g., in infants, when measurements have to be performed through a face mask.

A service mapping approach to the analysis of service use for people with acquired brain injury

This research study is a retrospective study which uses a novel graphical approach to visually present information about the duration and types of services provided to people with acquired brain injury in a university teaching hospital. It illustrates a method for using practitioners' knowledge of this client group and requisite interventions to develop a method of documenting the intensity and extensiveness of social work intervention. It provides a useful tool for social work, particularly in interdisciplinary settings, where the social work role in areas such as case management and counselling is rendered less visible by factors such as exception-based reporting which discourages detailed documentation of practice processes and outcomes.

Respiratory transfer impedance between 8 and 384 Hz in guinea pigs before and after bronchial challenge

We report a forced oscillatory technique for noninvasively measuring respiratory transfer impedance (Ztr) between 8 and 384 Hz in guinea pigs. This technique uses a device consisting of two chambers: one surrounding the animal's head that is used as a plethysmograph to measured flow through the airway opening and the other that surrounds the animal's body and is used to apply pressure oscillations to the body surface. Ztr was measured in spontaneously breathing awake guinea pigs and while the animals were anesthetized in normal and methacholine-challenged conditions. An eight-element model consisting of an airway compartment separated from a tissue compartment by a shunt gas compression compartment was fit to the data. Anesthesia increased central and peripheral airway resistance and bronchial airway wall compliance by 13, 31, and 44%, respectively, whereas it decreased tissue compliance by 37%. Compared with the unanesthetized condition, the methacholine challenge (20 micrograms/kg) resulted in an increase in central and peripheral airway resistance (69 and 319%, respectively) and a decrease in bronchial airway wall and tissue compliance (37 and 79%, respectively). This technique is capable of measuring Ztr in anesthetized and awake guinea pigs. Analysis of these data with this eight-element model provides reasonable estimates of airway and tissue parameters.

Interpretation of respiratory input impedance in healthy infants

Respiratory input impedance (Zin) is a potentially informative test of pulmonary function in infants who are unable to perform standard tests commonly performed in children and adults Analysis of Zin in dogs using the six-element model of DuBois et al. (J Appl Physiol 8:587, 1956) provides estimates of airways resistance separate from tissue resistance, as well as an estimate of thoracic gas volume. However, reliable estimates of these parameters can only be obtained when Zin displays a distinct antiresonance that is associated with the tissue inertance and alveolar gas compression compliance. To determine whether infants have such an antiresonance. Zin was measured in nine healthy infants (4 < f < 160 Hz). An antiresonance was found at 112.8-10.4 Hz, and the six-element model fit these data well, but the resulting parameters were physiologically unrealistic. We hypothesized that the antiresonance in the measured Zin is the result of shunt compliance proximal to alveolar gas compression compliance. Gas compression in the face mask and nonrigid upper airway walls could provide such a shunt compliance. We investigated another model with four parameters, a single shunt compliance (Cim) representing gas compression in the face mask in parallel with the infant's total respiratory resistance (Rrs) inertance (Irs), and compliance (Crs). This model fits the data well, and the estimated R, (19.3, 4.2 cmH O/L/s) was physiologically reasonable. However, Crs (Crs 1.03-0.58 mL cmH2O) was one order of magnitude smaller than reported Crs. The value for Cim was slightly larger than that based on the estimated volume of gas in the face mask, suggesting an additional influence of upper airway wall shunting. Computer simulations using a model that includes the face mask and upper airway walls confirmed that Cim and the upper airway wall properties significantly influence Zin data over this frequency range. Nevertheless, these simulations suggest that the Rrs estimated from the four-element model is related to airway resistance.

Diminished expression of CYP1A1 in urethane-induced lung tumors in strain A/J mice: analysis by in situ hybridization and immunohistochemical methods

We have investigated the regulation and expression of CYP1A1 in solid and papillary lung tumors induced by the carcinogen urethane. Female strain A/J mice were administered urethane (1 mg/g body wt) intraperitoneally, and when lung tumors were established at 16 weeks, mice were treated with 3-methylcholanthrene to induce CYP1A1. CYP1A1 mRNA was detected by in situ hybridization with a 3H-labeled RNA probe and quantitated by image analysis, whereas CYP1A1 protein was detected by immunohistochemical staining with an avidin-biotin complex procedure. Our results showed that in untreated control and tumor-bearing mice, the CYP1A1 mRNA was present at low levels, but the CYP1A1 protein was not detectable. Treatment with 3-methylcholanthrene induced increased levels of both CYP1A1 mRNA and protein in lung parenchyma and tumor foci. This induction was markedly higher in the parenchyma of control and tumor-bearing lungs than in either solid or papillary tumors. Differences in CYP1A1 mRNA and protein expression were not evident in solid and papillary tumors. In the parenchyma, induced CYP1A1 mRNA and protein were localized in the endothelial and alveolar septal cells. Endothelial cells in tumors also contained substantial CYP1A1 mRNA and protein, whereas low levels of both were found in lung tumor cells. Our finding of significant reduction in inducibility of CYP1A1 protein in conjunction with reduced CYP1A1 mRNA in tumor foci suggests reduced transcriptional activation as a regulatory mechanism. The lack of association between diminished CYP1A1 expression and either the tumor type or the mechanism mediating metabolic activation supports the hypothesis that the persistence of lung tumors may be due, in part, to a restricted capability for the formation of reactive intermediates.

Serial distribution of airway diameters from input impedance and computed tomography

Indirect measures of airway diameter such as respiratory system input impedance (Zin) have been widely used to infer or quantify bronchoconstriction, or bronchodilation. One such measure, Zin above 100 Hz has been shown to be primarily influenced by airway geometry and airway walls but not by lung and chest wall tissues. We used a recently developed method based on a complex asymmetrically branched network of tubes with nonrigid walls to analyze Zin from 100 to 2,000 Hz in control and bronchoconstricted (histamine injection) dogs. The resulting estimates of airway diameters indicated that peripheral airways were constricted far more (approximately 30% of their control diameters) than central airways (i.e., 0% in the trachea). Separate measurements of changes in airway diameters were made in an excised dog lung using high resolution computed tomography. The observed changes in airway diameter between lung volumes of total lung capacity (TLC) and functional residual capacity (FRC) were quantitatively consistent with those obtained from Zin data in our control dogs at FRC. We conclude that this systems identification method can be used to estimate the distribution of airway diameters from Zin.

Wave speed during maximal expiratory flow and phase velocity from forced oscillations

To test the hypothesis that pressure waves in the airways propagate at the speed obtained from maximal expiratory flow we compared wave speeds (WS) associated with flow limitation and phase velocities (PV) of oscillatory pressure waves in four excised calf tracheae for transmural pressures (Ptm) between 0 and -10 kPa. WS was calculated from static area-Ptm curves using the acoustic reflection technique. PV was determined by the forced oscillation method between 16 and 1024 Hz. WS ranged from 80 to 120 m/sec slightly increasing with decreasing Ptm. PV was relatively constant between 60 and 160 AZ with values between 170 and 310 m/sec. With decreasing Ptm, PV also increased, however, at 100 HZ it was 1.5-2.5 times higher than WS at all Ptm. In one additional trachea we found that PV decreased from approximately 200 m / sec at 7 Hz to approximately 130 m / sec at 0.23 Hz approaching WS. We suggest that VP is larger than WS because of the differences in airway wall mechanics during small-amplitude oscillations and large amplitude oscillations and large amplitude unidirectional wall motion such as a forced expiration. These results may provide an additional explanation why expiratory flow during rapid breathing or expiratory transients can exceed the maximum expiratory flow-volume envelope.

Acute viral infections

There have been important recent advances in the diagnosis of acute viral infections of the nervous system. Polymerase chain reaction amplification of nucleic acids in cerebrospinal fluid and tissues is a rapid and accurate tool in the diagnostic evaluation of patients with suspected infections. It has proved to be highly valuable in the noninvasive diagnosis of herpes simplex virus encephalitis and also in establishing the role of herpes simplex virus infection in Mollaret's meningitis. Improved diagnosis of herpesvirus infections should lead to more appropriate antiviral therapy and better outcomes.

Accuracy, reproducibility, and variability of portable peak flowmeters

The accuracy, reproducibility, and variability of seven commercially available peak flowmeters were assessed using the pulmonary waveform generator as recommended by the American Thoracic Society. The standard models were tested for peak flows of 100, 200, 320, 500, and 700 L/min. The low-range models were tested for peak flows of 80, 150, 200, 250, and 320 L/min. Most of the units provided highly repeatable estimates of peak flow. However, the accuracy of several devices (Assess [Healthscan Products, Cedar Grove, NJ] and Mini-Wright [Clement Clarke International, Harlow, Essex, UK] low-range models, and the Ferraris [Ferraris Medical, Holland, NY] and Mini-Wright standard-range models) did not meet the National Asthma Education Program (NAEP) recommendations. The device with the best performance in terms of accuracy, variability, and reproducibility, and the only one in which all units tested met the NAEP recommendations, was the Astech (Center Laboratories, Port Washington, NY) full-range model.

In situ hybridization analysis of hepatic cytochrome P450 2E1 messenger ribonucleic acid in mice. Modulation of expression by acetone

BACKGROUND

Cytochrome P450 2E1 is a distinct enzyme induced by diverse agents and notably by solvents including acetone. The P450 2E1 apoprotein is predominantly localized in the centrilobular region of the hepatic lobule in the constitutive state and after induction with acetone. In this study, we investigated the level and pattern of distribution of the 2E1 mRNA within the hepatic lobule in control mice and in mice exposed to acetone under acute and chronic conditions.

EXPERIMENTAL DESIGN

Male CD-1 mice were administered acetone acutely (5 ml/kg) or chronically (1% in drinking water for 8 days). Cytochrome P450 2E1 mRNA was detected in liver tissues, using in situ hybridization with a 3H-labeled RNA probe coupled with quantitative image analysis.

RESULTS

Acetone exposure did not alter the distance spanning a central vein and an adjacent portal vein. In control mice, 2E1 mRNA transcripts were localized most abundantly in the centrilobular zone of the hepatic lobule; intermediate levels were found in the midzonal region, and minimal levels were found in the periportal region. In acetone-treated mice, 2E1 mRNA expression within the hepatic lobule was significantly reduced and was manifested, firstly, in a decreased hepatocyte population with high expression, as assessed by reduction of total acinar areas containing 2E1 mRNA transcripts, and, secondly, in reduced 2E1 mRNA content within the hepatocytes. These alterations were observed to a significantly greater extent in mice after chronic versus acute acetone exposure.

CONCLUSIONS

Our results showed that acetone exposure in mice results in both a reduction and a more restricted distribution of 2E1 mRNA within the hepatic lobule. Furthermore, these findings suggest that 2E1 enzyme induction is associated with post-transcriptional events that are more marked after chronic than after acute exposure.

Serial distribution of airway mechanical properties in dogs: effects of histamine

We measured respiratory input impedance (Zin; 8-2,048 Hz) in five dogs (anesthetized, tracheostomized, vagotomized, and mechanically ventilated) during 80 s of apnea after a bolus intravenous injection of saline or histamine (5.0 mg). In the control case, three antiresonances in Zin were found in four of the dogs, whereas in the remaining dog only two were found. The magnitude and frequency of these antiresonances were significantly altered after bronchoconstriction. To interpret Zin, a model incorporating detailed airway geometry, asymmetrical branching, and nonrigid airway walls was developed. The model fit both the saline and histamine Zin data well and predicted a serial distribution of bronchoconstriction consistent with known effects of histamine; i.e., the diameters of the most peripheral airways were reduced (26% of their control values), whereas tracheal diameters were not significantly affected. The model provided estimates of tracheal diameters that were well correlated (r = 0.92) with direct measurements. Control estimates of soft tissue viscosity (1.63 +/- 0.42 cmH2O.s) and Young's modulus (406 +/- 125 cmH2O) compared closely with values in the literature. These results indicate that bronchoconstriction induced by histamine results in significant changes in Zin over this frequency range and that by using this data analysis approach definitive physiological parameters relative to airway geometry and wall mechanical properties can be obtained from measurements made at the airway opening.

Airway geometry and wall mechanical properties estimated from subglottal input impedance in humans

We measured input impedance between 16 and 2,048 Hz in intubated subjects at functional residual capacity. The corresponding subglottal impedances (ZSG) were then computed using a model where the endotracheal tube was represented by a distributed-parameter two-port network. ZSG was well described by a model based on Horsfield's asymmetric airway geometry at total lung capacity (TLC) with nonrigid walls. The walls of the cartilaginous airways included separate cartilage and soft tissue compartments, whereas the noncartilaginous airway walls had only a soft tissue compartment. Both compartments consisted of a series resistance, inertance, and compliance, the values of which were computed from airway dimensions and wall material properties (viscosity, density, and Young's modulus). Airway wall thickness was determined by scaling an airway wall area-diameter relationship. Airway lengths and diameters were scaled from the Horsfield TLC values by a single factor and by an order-dependent sigmoidal curve, respectively. The estimated soft tissue viscosity and Young's modulus were 1.04 +/- 0.21 cmH2O.s and 593 +/- 319 cmH2O, respectively. Airway lengths and tracheal diameters were not statistically different from the Horsfield values. The estimated diameters of the more peripheral airways were significantly reduced compared with the Horsfield TLC values (e.g., approximately 40% at the terminal airway), which is consistent with the reduction in airway caliber when the lung deflates from TLC to functional residual capacity. These results indicate that high-frequency ZSG is sensitive to subglottal airway geometry and wall properties and that by use of appropriate structural models one can estimate airway geometry and airway wall parameters.

Acoustic rhinometry in the evaluation of children with nasal or oral respiration

The purpose of this study was to determine if there are any differences in the nasal geometry of children with nasal respiration or predominantly oral respiration (mouth breathing). The technique utilized was the acoustic reflection technique or acoustic rhinometry. Acoustic rhinometry is a non-invasive method, which can be easily applied to young children. Twenty children participated and both nostrils were evaluated. Statistically significant differences were found in the total nasal volumes between the two groups, with the mouth breathers presenting with reduced nasal volumes. No differences were observed in the nasal cross sectional areas.

Cholinergic system in experimental rabies in mice

A defect in cholinergic synaptic neurotransmission could explain the neuronal dysfunction that has been observed in rabies. The enzymatic activities of choline acetyltransferase (ChAT), acetylcholinesterase (AChE), and enolase were assessed in the brains of rabies virus strain CVS-infected and uninfected mice. No statistically significant differences in activities of ChAT, AChE, or enolase were observed in the cerebral cortex or hippocampus of moribund CVS-infected mice versus controls. Binding to muscarinic acetylcholine receptors, which was assessed with 3H-labelled quinuclidinyl benzylate (QNB), was also not significantly different in the cerebral cortex or hippocampus of CVS-infected mice and uninfected controls. The studies suggest that dysfunction of the cholinergic system is unlikely of fundamental importance in this mouse model of rabies.

Wave propagation, input impedance, and wall mechanics of the calf trachea from 16 to 1,600 Hz

Propagation of waves in the airways is important in flow limitation as well as in oscillation mechanics. In five excised calf tracheae, we measured phase propagation velocity (c) and input impedance with open (Zop) or closed end (Zcl) for frequencies (f) between 16 and 1,600 Hz at two axial tensions [nonstretched (TN) and stretched (TS); TS > TN]. From 16 to 64 Hz, c slightly increased because of the viscoelastic properties of the wall tissues. Between 64 and 200 Hz, c was relatively constant and less than the free-field speed of sound (c0 = 340 m/s), with values smaller at TS (140 +/- 39 m/s) than at TN (172 +/- 35 m/s). Above 200 Hz, c exceeded c0 and displayed two maxima at approximately 300 and approximately 700 Hz, with values of approximately 360 and approximately 550 m/s, respectively. For f > 1,400 Hz, c approached c0. We provide evidence that the two maxima in c were the result of the two-compartment behavior of the wall tissues, i.e., the separate cartilaginous and soft tissues. A nonrigid tube model with its wall impedance composed of two series resistance, compliance, and inertance pathways in parallel simultaneously fits c, Zop, and Zcl well and hence provides a link among these data. By use of the relationship between volumetric wall parameters and the tracheal geometry, separate material properties such as viscosity and Young's modulus of both the soft tissue (approximately 1 cmH2O.s and approximately 0.26 x 10(4) cmH2O, respectively) and the cartilage (approximately 3.7 cmH2O.s and approximately 2 x 10(4) cmH2O, respectively) were estimated. These results indicate that measures of c and Zop or Zcl data over these frequencies provide information about the dynamic mechanical properties of both the soft tissue and cartilage in the airway walls.

Large granular lymphoproliferative disease associated with nephrotic syndrome, renal failure and leukoencephalopathy

A 23-year-old black female presented with general malaise, headache, high white cell count (136 x 10(9)/L), thrombocytopenia and nephrotic syndrome. She proved to have large granular lymphoproliferative disease with a natural killer cell phenotype and without a clonal rearrangement of the T-cell receptor genes. Renal biopsy demonstrated focal segmental glomerulosclerosis (FSGS). She developed a monophasic neurological illness, and rapidly became comatose six days after the initiation of high dose prednisone therapy. Computerized tomography of the brain showed marked hypodensity of the subcortical white matter. She regained consciousness subsequently, but died six months after her initial presentation with uncontrolled lymphocytosis and renal failure. Autopsy revealed FSGS with glomerular collapse and microcystic dilatation of the renal tubules, and there was perivascular demyelination in the subcortical white matter of the brain. We speculate that lymphokines released by the natural killer cells may have played an important role in the pathogenesis of both the nephrotic syndrome and leukoencephalopathy.

Branching airway network models for analyzing high-frequency lung input impedance

The input impedance of the lung (Zin) at high frequencies (> 100 Hz) is a complex function of the airway geometry and the mechanical properties of the airway walls. To investigate how the purely geometrical factors influence Zin, we measured Zin between 16 and 1,520 Hz in six dried dog lungs with the forced oscillation technique. In each of the lungs we found three resonances, at 36 +/- 5, 648 +/- 100, and 1,289 +/- 150 Hz, and at least two antiresonances (relative maxima in the real part of Zin), at 372 +/- 60 and 1,105 +/- 110 Hz. These data were fit with models featuring a detailed asymmetric branching network of the airways obtained from morphometric data published by Horsfield et al. (J. Appl. Physiol. 52: 21-26, 1982). On the basis of low-frequency (< 100 Hz) data alone, we first established a model of the acini, which was then attached to the end of the airway branching model. With a single scaling factor for the radius and length of the airways, the fit was unsatisfactory. Using sensitivity analysis techniques we determined which candidate variables of the structural model could influence Zin in a manner to improve the fit. We found that a two-parameter model accounting for separate central and peripheral airway diameter scaling provided a reasonable fit to Zin. On average the model required central diameter scaling close to unity (0.94 +/- 0.09), and the peripheral diameter scaling factor was 0.87 +/- 0.38. Over a range of parameter values that we believed were physiologically reasonable (i.e., scaling factors between 0.5 and 1.5), a single set of parameter values was found in all lungs. These results suggest that structurally based inverse models of Zin that include multiple antiresonances may provide information about airway geometry.

Impact of frequency range and input impedance on airway-tissue separation implied from transfer impedance

In humans, application of the DuBois (DuBois et al. J. Appl. Physiol. 8: 587-594, 1956) six-element model to respiratory transfer impedance (Ztr) data has been proposed as a means to noninvasively estimate airway and tissue properties. This approach requires prior knowledge of alveolar gas compressibility (Cg). With input impedance (Zin), prior knowledge of Cg is not required, but the data do not support a reliable separation of airway from tissue properties. In this study, we investigated the separation of airway and tissue properties when Ztr and Zin data are measured and analyzed simultaneously over a larger frequency range than usual. In 10 healthy adults, we measured Ztr and Zin from 2 to 64 Hz. Zin was measured using both the standard approach with oscillations directly into the airway opening (Zst) and the head generator approach (Zhg) with oscillations applied around the head. With Ztr data alone, we found that the airway resistance and inertance estimates were reliable with only 2- to 32-Hz data and were unaffected by including the additional 32- to 64-Hz data. Conversely, the estimates of tissue resistance and inertance were highly unreliable unless the 32- to 64-Hz data are included. Because of enhanced sensitivity of Ztr to Cg from 32 to 64 Hz, inaccuracies in the assigned Cg will distort the estimated tissue but not airway properties. The Ztr-based parameters predicted Zhg data far better than Zst data, which is consistent with Zhg data being less influenced by upper airway shunting over this frequency range. There was no apparent advantage to combining Ztr and Zhg data during parameter estimation. With Cg unfixed, the estimated Cg was 50-100% higher than expected from an independent measurement of functional residual capacity. These results confirm that Ztr alone can provide a reliable distinction of lumped respiratory airway and tissue properties that are little influenced by upper airway wall shunting but only if 2- to 64-Hz data are analyzed. This distinction, however, requires an accurate prior measurement of Cg, and this requirement cannot be removed by combining Ztr and Zin data.

Experimental infection of Aedes aegypti (Diptera: Culicidae) by the oral route with Sindbis virus

The infectivity, dissemination, and transmissibility of wild-type Sindbis (SIN) virus were studied in Aedes aegypti (L). There was an initial decline in the viral titer of whole mosquitoes for 3 d after ingestion of virus, followed by a gradual increase to a maximal level by day 6. Immunoperoxidase staining of Ae. aegypti for viral antigen showed infection of midgut epithelial cells on day 1, of the fat body by day 3, and of the brain by day 4. By day 5, there was infection of the foregut, hindgut, Malpighian tubules, ovariole sheaths, Johnston's organ, thoracic ganglia, ventral nerve cord, and salivary glands. Viral antigen was not detected in the flight muscles and was found only in ovariole sheaths of the ovaries; germinal tissue was not infected. The transmission rate from SIN-infected Ae. aegypti to neonatal mice was 40%. A comparison of Ae. aegypti infected with SIN and with a neuroadapted strain of Sindbis virus (NSIN), which is more neurovirulent than SIN to mice after intracerebral inoculation, did not reveal significant differences in infectivity, dissemination, or transmissibility. The important differences between SIN and NSIN in a mouse model were not reflected in the infection of Ae. aegypti by the oral route.

Total respiratory input impedance with the upper airway wall shunt minimized

Respiratory impedances (Zrs) measured with the cheeks manually supported (Zsc) demonstrate an antiresonance (AR) at approximately 170 Hz, whereas those measured with the head generator (Zhg) have an AR at significantly lower frequencies (150 Hz). The differences in the AR between methods were previously attributed to upper airway wall (UAW) shunting in Zsc, and Zhg was believed to represent shunt-free impedance. To test this hypothesis, we measured four independent estimates of Zrs (4-256 Hz) in five healthy adults. Applying the oscillations at the mouth, we measured Zrs with the cheeks unsupported (Zuc) and when the subject's head and neck were enclosed in a rigid chamber completely filled with water (Zwa). We also measured Zhg with the oscillations applied around the head. Because water is incompressible, Zwa should minimize UAW shunt if not completely eliminate it. There were no significant differences in any of the AR features (e.g., location and bandwidth) of Zuc, Zsc, and Zwa. Conversely, all AR features of Zwa and Zhg were significantly different. To assess wall motion during both forms of oscillations (i.e., applied at the mouth and around the head), we measured two UAW local impedances by use of accelerometers placed on the cheeks (Zch) and submental (Zsm) region. Above 40 Hz, Zch and Zsm estimates were significantly dependent on the forcing method. Furthermore, Zch and Zsm made with the standard oscillations were consistent with the lumped UAW impedances measured with a head plethysmograph, whereas those made with the oscillations around the head were not. Therefore we conclude that, at > 32 Hz, Zsc more closely represents shunt-free impedance than does Zhg and hence should be preferred when Zrs are measured.

Respiratory input impedance from 4 to 256 Hz in normals and chronic airflow obstruction: comparisons and correlations with spirometry

Measurement of respiratory system input impedance (Zrs) by forced oscillation (FO) has generally been limited to frequencies less than or equal to 50 Hz, and correlations with spirometry have been variable. Using FO from 4 to 256 Hz in normals, Jackson and colleagues recently described a first acoustic antiresonance frequency (Far,1) at approximately 170 Hz. Using the same frequency range, we compared several Zrs spectral characteristics with spirometry in 12 chronic airflow obstruction (CAO) patients (range FEV1 0.8 to 2.0 L) and 10 matched controls. Compared with controls, patients had a higher first resonance frequency (Fr,1) (mean +/- SD = 15 +/- 5 versus 10 +/- 2 Hz, p less than 0.02) and a higher Far,1 (196 +/- 11 versus 172 +/- 13 Hz, p less than 0.0002). Good correlations occurred between % predicted FVC and the Far,1 (r = -0.81, p less than 0.0000), between FEV1/FVC and the reactance at 20 Hz (r = -0.6, p less than 0.003), between FEV1 and Far,1 (r = -0.74, p less than 0.0001). Because Far,1 may be affected by airway wall mechanical properties, the shift in Far,1 seen in these patients may be due to airway wall properties in CAO. We conclude that measurement of Zrs up to 256 Hz requires little patient cooperation and may be clinically useful. It can differentiate CAO patients from controls and correlates well with spirometry. The first acoustic antiresonance frequency may reflect airway mechanical properties and provide information not available from Zrs measured at lower frequencies.